Author's note: I have recently found that some Schellhas classification charts list God A as a different alphabet letter. However, several resources connected to places of higher learning state that God A's alphabetical designation is A.
God A, -- called Kisin (also spelled Cizin) in the Madrid Codex -- is an ancient Maya god of death, associated with putrefaction as well as gas produced by human beings (flatulence). He is associated with the owl, as the ancient Maya connected the owl with caves (Xibalbá -- the underworld -- was understood to be underground), night and killing prey.
Kisin translates as "Stinking One" or "Flatulent One" (the modern Yucatec Maya word for fart is "kis".) This isn't just a modern name for God A, it is also the understood to be an ancient name.
In the ancient Maya writing system, Kisin's name was written two ways: one way depicts a dead body whose eyes are closed, and the second way depicts Kisin's head but with a short nose and bone jaws and a sacrificial knife.
Ancient Maya artists sometimes depicted Kisin as a skeleton in motion -- understood to be dancing --, sometimes with large spots who is holding something that resembles a lit cigarette. Other times Kisin was drawn as a bloated figure whose chest has sores and whose skin in general has dark jagged spots.
Another part of Kisin's appearance is his "costume". Kisin was drawn wearing as a neck collar. This collar was made of what the book Handbook to Life in the Ancient Maya World describes as "extruded eyes" and gives the name of "death eyes" -- possibly eyes and their nerve cords. Alternately, instead of a collar, Kisin would be depicted as having hair or cuffs on his wrists and ankles made of the death eyes.
Kisin ruled Xibalbá, controlled earthquakes, and was also the patron of the day Kimi (a day whose name means death.) In the codices he can be seen in scenes connected with human sacrifice, next to one of the Maya war gods. At times in the codices he is shown killing trees that Chac (God B) had planted.
Kisin may not have just been one god, but one aspect of a god. In this theory, this multiple-aspect god had other guises as well as names, including Ah Puch, Yum Kimil and Xibalbá.
Missouri State University: MAYA GODS AND GODDESSES
"Historical Dictionary of Mesoamerica"; Walter R. T. Witschey, Clifford T. Brown; 2011
"A Mythological Reference"; G. Rodney Avant; 2005
Encyclopedia of religion: Volume 1"; Lindsay Jones; 2005
Encyclopedia Britannica: Cizin
"Handbook to Life in the Ancient Maya World"; Lynn V. Foster; 2005